1. Field of the Invention
The invention relates to an improved process for connecting a thin transparent electroconductive layer deposited on a sheet of silicate glass, and particularly to a thin layer serving as a heating resistor on a glazing having electric heating.
2. Discussion of Background
Glass sheets having an electroconductive transparent coating are used in particular as heated glazings and may be utilized for various purposes such as antenna glazings, heated if applicable; windows having an electromagnetic shielding role, etc.
The laying or depositing of the connectors receiving the connecting wires (e.g. to couple the heating or electroconductive layer to a voltage source) involves a delicate operation. In most cases, it is first necessary to provide a collector for distributing the current along the edges opposite the conductive zone, however, on the heated glazings the most severe or difficult requirements are often encountered. Heated windshields of motor vehicles, for example, must have a high transparency, greater than 70% in the visible spectrum, and at the same time exhibit only a slight surface resistivity, of a few ohms per square cm. Their conductive layers (which are extremely thin because of the required transparency, and consequently are vulnerable), are then stressed almost to their load limit by a relatively high current density. The connection must provide, in the transition zone, an electric contact that is even and of good quality, to prevent any local surge of current.
The connection is particularly problematic when the thin layer itself consists of a film of a metal, such as silver, placed between semiconductive or nonconductive layers of metal compounds protecting it from outside influences and attenuating the reflectivity. Deposited by various processes, such layers with protective layers of metal oxides, whose total thickness is at most on the order of a micron, are today in common use.
Multiple solutions have therefore been proposed to connect these thin transparent layers. They consist essentially in reinforcing the concerned marginal zone with a conductive strip that is clearly thicker consisting, for example, of a silver-based electroconductive enamel and/or of a coating obtained by metallization, that can be deposited before or after the transparent layer, in particular to constitute the collector. The reinforced strip will then receive, preferably outside the layer, a connector soldered with a tin-based brazing, or will even be able to be doubled with a conductor for distribution of the current, wire or braid soldered from spot to spot or thin metal foil glued or merely pressed on the carrier sheet.
Each of these solutions has its own advantages and drawbacks in effectiveness, adherence, optical appearance, cost, durability, etc.